In a new Zend Framework related post to his blog today Rob Allen takes a look at a different operating mode he found with Zend_Date changing how it handles format specifiers.
I discovered recently that Zend Framework 1's Zend_Date has two operating modes when it comes to format specifiers: iso and php, where iso is the default. When using Zend_Validate_Date in forms, I like to use the php format specifiers as they are what I'm used to and so can easily know what they mean when reviewing code that I wrote months ago.
His example code shows how you can use the standard date formatting strings in a Zend_Form validator (the "php" format) and an example using the Zend_Date::MONTH or Zend_Date::YEAR identifiers (the "iso" format). He also shows how he met two other requirements - validation for empty and a consistent format on the date validation ("Y-m-d").